This invention provides a low cost disposable filter dispenser which quickly and conveniently separates and dispenses a small quantity of fluid such as blood plasma or blood serum which may be used for laboratory analysis or other purposes. This new filter dispenser minimizes the possibility of attendant contamination while in no way adding to the inconvenience of a donor.
Despite numerous attempts to automate the process of drawing blood samples and separating plasma or serum therefrom for analysis, the process remains essentially manual. In contrast, much greater success has been attained in automating the analysis of the samples once they have been drawn and separated.
At the present time, the most commonly used procedure for drawing blood samples starts with use of a cylindrical holder 10 and an evacuated container 11 called a "Vacutainer," as illustrated in FIG. 1. The generally cylindrical holder has a closed end 12A and an opposite open end 13B for receiving the container 11. A plastic support 13 is molded around a double ended phlebotomy needle 14 near its center and threadingly engages the closed end 12A of the holder 10. The plastic support 13 has a bulbous protrusion 15 on its interior end, which receives in tight fitting relationship an upper end of a rubber sock 16. Normally, the closed end of the sock 16 encompasses and protects the end of the needle 14 retained in the holder 10.
In operation, the holder 10 is used when inserting the outer end of the needle 14 into a vein of a donor. At this time, sock 16 serves to prevent leakage of blood into the interior of holder 10. Next, the evacuated container 11, having a rubber stopper 17, is inserted, stopper end first, into the open end of holder 10. The intension end of the needle 14 forced through the rubber stopper piercing both the rubber sock 26 and stopper 17. The vacuum within container 11 then causes blood to be withdrawn through needle 14 and into the container 11. Typically, several of these "Vacutainers" may be successively inserted into the holder 10 and filled with blood before the outer end of needle 14 is withdrawn from the donor.
When different containers have been filled, they are then typically used for different analytical tasks. For example, one container might contain an anticoagulant such as tri-sodium citrate, ACD or heparin and have plasma separated therefrom. In another container the blood might be allowed to clot so that serum can be separated for analysis.
Once the samples are drawn, they are typically labeled and sent to a laboratory. At the laboratory, the containers are centrifuged for 5-10 minutes at 900-2000 g's. A laboratory technician must then carefully remove the rubber stopper 17 from its container 11 without disturbing the contents. A disposable non reusable pipette is used to draw off plasma or serum and the rubber stopper 17 is placed back in the container 11 prior to disposal of the container 11 and its contents.
This widely used procedure is thus quite slow, and inconvenient. Both the person drawing blood and the laboratory technician are exposed to possible contamination. The needle, the "Vacutainer", the pipette and a tray or dish receiving the analysis fluid from the pipette must all be disposed of, adding to costs.
U.S. Pat. No. 4,343,705 for "Biological Liquid Fractionation Using Opposite Flow Directions Across A Membrane" by Legg teaches one attempt at improving upon the blood withdrawal and separation process. Legg pours the blood into an open receptacle from which it is aspirated back and forth across one side of a flat sheet membrane filter. The other side of the filter communicates with the receptacle for the plasma filtrate. The system requires expensive pumps, valves and automatic controls. The disposables include the receptacles and the filter membrane, and are thus relatively expensive. The laboratory technician has essentially the same risk of contamination as where the centrifuge and pipette are used.
Many attempts have been made to incorporate the fractionation process directly into the "Vacutainer" or similar receptacle. Examples of U.S. patents describing such attempts are listed as follows:
3,508,653 Coleman PA0 3,539,300 Stone PA0 3,682,596 Stone PA0 3,761,408 Jae Yoon Lee PA0 3,814,079 LeRoy, Sr. PA0 3,850,174 Ayres PA0 3,920,557 Ayres PA0 3,926,521 Ginzel PA0 3,960,727 Hochstrasser PA0 3,965,889 Sachs PA0 3,972,812 Gresl, Jr. PA0 4,012,325 Columbus PA0 4,035,294 Landers et al PA0 4,052,320 Jakobowicz PA0 4,083,788 Ferrara PA0 4,131,549 Ferrara PA0 4,303,530 Shah et al. PA0 4,443,345 Wells
In each case, high cost, inconvenience of use or some other disadvantage has prevented the disclosed technique from receiving widespread acceptance. It is desirable to employ the widely accepted vacuum enclosure approach for withdrawing blood, but it is far preferable to be able to fractionate the needed small amounts of filtrate directly on site, virtually immediately and without additional handling.
It is known to use a rotary system in conjunction with a membrane filter to fractionate a liquid suspension so as to obtain a desired filtrate with high throughput, reliability and freedom from contamination. One example of such a system is shown in application Ser. No. 591,925 filed Mar. 21, 1984 by Donald W. Schoendorfer for "Method and Apparatus for Separation of Matter". In this system the rotary spinner, which may include a surface filter membrane or be encompassed at least in part by a filter membrane, is arranged and operated to establish enhanced vortices of the Taylor type, which provide a constant sweeping motion over the filter membrane together with high shear to establish a high throughput, non-clogging filtration action. This system is particularly effective in hemapheresis applications because it employs a low cost, non-contaminating disposable that does not hemolyze or otherwise damage the fragile blood constituents. However, this disposable still has much greater capacity and a larger and therefore more costly membrane area than are needed for most clinical applications. Even if scaled down it would require a separate procedure to transfer blood and larger and more extensive drive, control and pumping units than are desired.